1. Field of the Invention
The present invention relates to a zoom lens for a single lens reflex camera, and particularly to a zoom lens which is capable of effecting focusing from infinity to an extreme near distance at any zoom position.
2. Related Background Art
Conventionally, there is provided for a single lens reflex camera a so-called macro lens which is capable of focusing from infinity to an extreme near distance with image magnification of about -0.5 to -1.
Also, there is provided a kind of zoom lens which additionally has a function capable of photographing with a shorter distance than an ordinary closest object distance, which is called a macro mechanism.
Or, there is provided a close-up lens which is attached to the object side of the photographing lens, in order to reduce the closest object distance.
However, either of the conventional macro lenses is a single focus lens, which requires an operation for changing a distance between an object to be photographed and the camera and, simultaneously, an operation for focusing, in order to change an image magnification. For this reason, it is troublesome to alter a photo composition when using a tripod for photographing an object at a close distance.
Also, a majority of the macro mechanism of a zoom lens can be used only at either one of the wide angle end (so-called wide macro) or the telephoto end (so-called tele macro), so that zooming can not be carried out at macro photographing. As a result, the operability of such lens is equal to or worse than that of a macro lens with a single focus. Moreover, the maximum image magnification of such lens is about -0.3, which is not sufficient when an object is to be photographed as a larger image.
Though some type of the macro mechanism of zoom lens allows close photographing at all zoom positions, the maximum image magnification in this case is about -0.25, which is also not sufficient when an object is desired to be photographed as a larger image.
When accessories such as a close-up lens and the like is used, such accessories are to be attached or detached, depending on whether an object to be photographed is at a far distance or a close distance, which is troublesome.